Astronomy Essentials

Earth farthest from the sun on July 5

A distant sunrise under light clouds, seen across rolling hills.
View at EarthSky Community Photos. | Ragini Chaturvedi, a frequent contributor to our pages, caught this sunrise from Palouse, Washington, on June 22, 2021, the day after the solstice. She wrote: “Encouraged by EarthSky community, I share another phenomenal view of Palouse, Washington. At the elevation of 3,612 feet [1,100 m], the Steptoe Butte State Park presents such a super early sunrise view. Breathtaking.” Thank you, Ragini!

Earth farthest from the sun

Planet Earth will reach a milestone on July 5, 2021, as it swings out to aphelion, our most distant point from the sun. It’s been a blazingly hot summer in parts of the Northern Hemisphere so far. Earth’s aphelion comes every July, in the midst of Northern Hemisphere summer (and Southern Hemisphere winter). So you know our distance from the sun doesn’t cause Earth’s seasons.

We’ll be precisely farthest from the sun at 22:27 UTC on July 5. That’s 5:27 p.m. Central Daylight Time in North America. Translate UTC to your time.

Looking for Earth’s exact distance from the sun at aphelion? It’s 94,510,886 miles (152,100,527 km). Last year, on July 4, 2020, the Earth at aphelion was a tiny bit closer, at 94,507,635 miles (152,095,295 km).

The fact is, Earth’s orbit is almost, but not quite, circular. So our distance from the sun doesn’t change much percentagewise (a little over 3%). Today, we’re about 3 million miles (5 million km) farther from the sun than we will be six months from now. That’s in contrast to our average distance from the sun of about 93 million miles (150 million km).

The word aphelion, by the way, comes from the Greek words apo meaning away, off, apart and helios, for the Greek god of the sun.

Apart from the sun. That’s us, on July 5.

What causes the seasons?

The seasons aren’t due to Earth’s changing distance from the sun. We’re always farthest from the sun in early July during northern summer and closest in January during northern winter.

Instead, the seasons result from Earth’s tilt on its axis. Right now, it’s summer in the Northern Hemisphere because the northern part of Earth is tilted most toward the sun. We’re receiving the sun’s rays most directly

Meanwhile, it’s winter in the Southern Hemisphere because the southern part of Earth is tilted most away from the sun. The more indirect sunlight causes cooler temperatures.

Read more: Why Earth has 4 seasons

Earth’s varying distance from the sun does affect the length of the seasons, though. That’s because, at our farthest from the sun, like now, Earth is traveling most slowly in its orbit. That makes summer the longest season in the Northern Hemisphere and winter the longest season on the southern half of the globe.

Conversely, winter is the shortest season in the Northern Hemisphere, and summer is the shortest in the Southern Hemisphere, in each instance by nearly five days.

Earth at perihelion and aphelion 2001 to 2100

Diagram showing Earth's orbit with aphelion and perihelion distances labeled.
Image via NASA.

Are Earth’s closest and farthest points tied to the solstices?

The short answer is no. It’s true that Earth is farthest from the sun every year in early July, about two weeks after the June solstice. And it’s true that Earth is closest to the sun every early January, about two weeks after the December solstice. Is it a coincidence? Yes, it is. Over the long course of time, the dates of Earth’s closest and farthest points to the sun shift with respect to the solstices.

According to timeanddate.com:

Due to variations in the eccentricity of the Earth’s orbit, the dates when the Earth reaches its perihelion or aphelion are not fixed. In 1246, the December solstice was on the same day as the Earth reached its perihelion. Since then, the perihelion and aphelion dates have drifted by a day every 58 years. In the short-term, the dates can vary up to two days from one year to another.

Mathematicians and astronomers estimate that in 6430, over 4000 years from now, the perihelion will coincide with the March equinox.

Solid yellow circle with thin rim of gray around it.
At aphelion, our most distant point from the sun, the sun does appear a bit smaller in our sky. This composite image illustrates the difference. This image consists of 2 photos, taken just days away from a perihelion (Earth’s closest point to sun) in January 2016, and an aphelion (Earth’s farthest point from sun) in July 2017. The gray rim around the sun (actually the perihelion photo) illustrates that, as seen in our sky, the sun is about 3.6% bigger at perihelion than aphelion. This difference is, of course, too small to detect with the eye. Photo by Peter Lowenstein of Mutare, Zimbabwe.
Three images of the sun appearing successively each a slightly different size.
Animation of the image above … the size difference of the sun between Earth’s perihelion (closest point) and aphelion (farthest point).

Bottom line: Planet Earth reaches its most distant point from the sun for 2021 on July 5. Astronomers call this yearly point in Earth’s orbit our aphelion.

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Why isn’t the hottest weather on the year’s longest day?

Posted 
July 4, 2021
 in 
Astronomy Essentials

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